1. Field of the Invention
The present invention relates to a plated copper alloy material as an electrically conductive material for connecting parts such as terminals, connectors and junction blocks, which are used for automobiles and consumer electric appliances.
2. Description of the Related Art
Connection of automotive wires is accomplished with tin-plated terminals of copper alloy. A pair of terminals (male and female) of engaging type constitute a connector. An assembly of such connectors is called a multipole connector.
The recent widespread use of electrical equipment in automobiles requires a single connector to have more terminals (or poles) than before. A connector with many poles needs a large physical force for insertion or even needs a special tool for insertion. This lowers the efficiency of assembling work. For this reason, there has been a demand for connectors which can be inserted with smaller forces than before even though the number of poles increases.
Tin-plated terminals permit insertion with smaller forces as the thickness of tin coating decreases. However, this advantage is lost when they are used for automobiles, in which most connectors have been removed from the cabin to the engine room in order to save the cabin space. The ambient temperature in the engine room reaches about 150° C. At such a high temperature, the thin tin-plating layer permits copper to diffuse from the copper parent material or (alloying element to diffuse from the copper-alloy parent material) or permits nickel to diffuse from the under-lying plating layer, to form an oxide on the surface of the tin-plating layer. This oxide increases the contact resistance of the terminals. The increased contact resistance makes electronic controllers to malfunction. In practice, therefore, it is difficult to reduce the thickness of the tin-plating layer while keeping electrical reliability.
Moreover, the tin-plating layer is subject to corrosion when automobiles are run or parked for a long time in industrial areas where air pollution with sulfur dioxide gas is prevailing. This corrosion reaches the copper alloy parent material, thereby impairing the reliability of the connecting terminals of engaging type.
A copper alloy material with a tin plating layer is used also as a conductive material in a junction block for an automobile. In implementation of electronics parts in the junction block, the material is required to undergo heat treatment at about 100° C. and further effect of heat by solder reflowing. Such conditions of heat do not exist in a conventional production process. Accordingly, the circumstances require a copper alloy material with a tin plating layer which maintains solder wettability after undergoing such heat effects. Furthermore, since the junction block is recently installed in an engine room instead of in a cabin in order to save space, the same problems as mentioned above arise.
A lead frame material with improved heat resistance is disclosed in Japanese Patent Laid-open No. 196349/1994. It consists of a parent material of nickel silver and a multi-layered coating film formed thereon by plating from nickel, copper-tin intermetallic compound, and tin. It was found that when the multi-layered coating film is formed on a copper alloy parent material according to the disclosure, the resulting terminals for engaging type need a large force for insertion, easily crack when bent sharply, or increase in contact resistance after reflowing.
In order to improve solder wettability, it is effective to make the thickness of a tin plating layer more than 2 μm which is thicker than that of a conventional material. However, electric reliability (a low contact resistance) can not be maintained after solder reflowing or after a long use in a high temperature only by controlling the thickness of a tin plating layer. Further, generation of pits in a tin plating layer can not be suppressed after reflowing process for producing a tin plated material.